Helmet



FIG. 1 is a front right perspective view of a helmet showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof; and,

FIG. 6 is a top plan view thereof.

The details shown in broken lines form no part of the claimed design. 

CLAIM The ornamental design for a helmet, as shown and described. 